What is my meter telling me?

[Edward R]

Well, I swiped a meter from work for the long weekend, a BK lcr meter to test some of my crude attempts at pickup making, to try to correlate what I hear to some analysis. It can test at 100hz, 120 hz, 1khz, and 10khz, and have the option to test Q, D, and something for degrees, whatever that may be...

Problem is, i don't know how to "read" the data. Or even if the test levels will work ok (I get no readings at 10khz). Shoot, i'm not even sure what C, Q, and D mean in relation to a pickup. I figured L is the power of the pickup, C would equate to brightness (lower = brighter). Not sure if my thinking is correct, or what Q and D even measure for a pickup.

Here are measurements for a P90 I did @ 1khz test level:

L : 7.957
C : 2.715
Q : 2.58
D : .386

Well, if you have any tips or tricks for a newb to understand what these are telling me, that would be great! Thanks

ER

[SkinnyWire]

L = Inductance. Presumably for a P-90, your reading indicates L = 7.957 Henries. The unit of inductance is the Henry.

C = Capacitance. I'd guess your reading is in the nano-Farad (10 to the power of -9) or pico-Farad (10 to the power of -12) range. I've never been able to make any sense of that particular reading at 1kHz for pickups, though I'm sure one of the really smart engineers here can explain it.

Q = Quality Factor. The higher the Q, the closer a coil is to performing like an "ideal" inductor (no losses, etc.). It's the ratio of the coil's inductive reactance to its resistance (series equivalent, I believe) at a given frequency. I don't really pay much attention to it, so I don't really know what to make of your particular value.

D = Dissipation Factor. It's basically 1/Q and sort of as power factor is in terms of AC circuit loading. So, if Q is high then D is low and losses due to inefficiencies (i.e. deviations from the ideal) would be minimized.

Aside from the DC resistance, the inductance and AC resistance can be helpful measures. I use them to look for variations from the norm, or what I expect to result from a particular coil.

[Joe Gwinn]

Well, I swiped a meter from work for the long weekend, a BK lcr meter to test some of my crude attempts at pickup making, to try to correlate what I hear to some analysis. It can test at 100hz, 120 hz, 1khz, and 10khz, and have the option to test Q, D, and something for degrees, whatever that may be...

What is the B+K model number?

Be aware that many LCR meters do not give accurate results with low-Q inductors like guitar pickups. Does this instrument claim to handle such lossy inductors?

Also be aware that you cannot measure the self-capacitance of a inductor simply by setting the LCR meter to read C. The resulting C value is meaningless.

No LCR meter can do this, unless it is able to compute using data from multiple test frequencies, which no B+K instrument does. While the B+K measures at multiple frequencies, it does not combine the data. Also, the 10 KHz data will likely prove useless, as pickups self-resonate around there.

Search the forum for the relevant discussion threads to find the details.

[Edward R]

Thanks for the info guys....

The BK is model # 879. I'm not sure if the meter claims to be able to low-Q pickups or not, I just grabbed it off a friends bench.

So I assume testing my pickups will prove useless with this style meter since it doesn't combine data? Or could I compute the data from different frequencies by myself witha mathamatical equation?

I don't know, just playing around.

Thanks for the replys!

ER

[Joe Gwinn]

The BK is model # 879. I'm not sure if the meter claims to be able to low-Q pickups or not, I just grabbed it off a friend's bench.

I looked up the 879 manual. It doesn't say.

The acid test is to take a good iron-cored inductor (like a choke or power transformer) in series with a 50 Kohm pot and measure the inductance of the assembly. As one raises and lowers the resistance by turning the pot shaft back and forth, what does the indicated inductance value do?

So I assume testing my pickups will prove useless with this style meter since it doesn't combine data? Or could I compute the data from different frequencies by myself with a mathematical equation?

A well-designed LCR meter can measure inductance and AC resistance (from which Q and D are computed) of a pickup. If you want to measure self-capacitance, you will need more equipment. Search the forum for the relevant threads, including those on measuring the self-resonance frequency of a pickup.


By the way, please edit your user profile to give your general geographic location.

[Edward R]

I searched through some of the previous threads about the capacitance and the resonant peak, but I don't really understand all that stuff as it is laid out in this forum, and was looking for some simpler explanations for help!

I was just seeing what I could figure out about my stuff with the meter I had available. Certainly didn't think it would give me a whole story, just some parts to the story.

As it has no bearing on the discussion, i'd rather not edit my user location. Thanks

ER

[belwar]

Really the most useful item you are measuring is inductance. I would focus your efforts on learning about inductance.

Two big factors that affect inductance are the ammount of metal in the pickup, and the type of metal. I believe number of turns on the bobbin also has an effect.

Higher inductance *usually* means a darker pickup. There are lots of ways to alter the inductance. For example switching from Alnico to Ceramic lowers the inductance. Other ways to alter inductance can be tochange pole piece alloys, remove or add a metal cover, remove or add a keeper bar.

I didnt use my LCR meter much until recently, now im using it more. Mostly for testing existing pickups that I want approximate the tone of. I'm working on a bass pickup that has very high inductance, and I'm adding or removing material until I get close to the original.

[Possum]

...

Inductance and AC resistance are the two most useful. AC resistance is logical in its readings, the higher it goes the darker the pickup is. Inductance often goes DOWN if you add more steel or a cover, its not real logical and easy to misinterpret. You need to take readings in the serial mode also. I'd be interested to know if you can get AC resistance readings at 10khz.

I've been using the peak resonance readings lately, but they don't tell you about a treble edge that can verge on shrill, that I am pretty sure is way above the peak resonance. All this shit can get really confusing. An LCR meter is really useful and the Extech is the best choice and most affordable, but it only goes to 1khz and there's alot that happens way above that it just plain doesn't see.

[Jeff Callahan]

Haven't read it all, but this seems on track. Damn, why didn't I go to college there?

Jeff

[Old Tele man]

Damn, why didn't I go to college there?

Jeff

..you're not the only person to have said those exact same words!